The B-1 was from Ellsworth AFB and practice-bombed (no real ordinance was expended) a school bus depot (yard) in Snyder, Texas.

Now using a little educated guesstimation based on the look of the yard on Google Maps - the school buses could have been a decent stand-in for mobile missile launchers and the building next to it the "missile maintenance" center.

You'll also notice they mention SA-6 and SA-8 - these are mobile ground-to-air missile launchers similar to this Russian example:

Wow you picked up on something big here I think. Clearly the US wasn't happy to see N. Korea acquire mobile launchers. If there is any provocation from them then I am sure the mobile's are a top priority to take out, even in a limited response situation.